An unusual translocation of immunoglobulin gene segments in variants of the mouse myeloma MPC11

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Abstract
Immunoglobulin light chain genes of the mouse are composed in germ-line DNA of four separate segments, the leader, V (variable), J (joining) and C (constant) segments. In immunocom-petent cells a V and a J gene segment are joined by a site-specific recombination event1,2 . In variants of the mouse myeloma MPC11 a so-called kappa (κ) light chain fragment is expressed3 which consists of the MOPC321 leader peptide, joined to the κ constant region peptide4,5. Using the Southern blotting technique6 we found that the gene coding for the light chain fragment has apparently been generated by an aberrant translocation of a V gene segment identical or very similar to the MOPC321V gene segment into the large intervening sequence between the J and the C gene segments. The resulting deletion of the splice signals of the J segments could be the reason for the observed splicing between leader and C region sequences, a phenomenon which may be of general interest for the understanding of the splicing mechanism.